Sound reproducing device



March 15, 1932. A. J. FL ECK SOUND REPRODUCING DEVICE Filed April 14, 1950 2 Sheets- Sheet l G oh 4% Z ATTORNEY March 15, 1932'.

A. J. FLECK SOUND REPRODUC ING DEVICE Filed April 14, 1930 i2 Sheets-Sheet 2 INVENTO'R ATTORNEY Patented Mar. 15, 1932 PATENT OFFICE ABRAHAM J. FLECK, OF BRADLEY BEACH, NEW JERSEY sonim nnrnonncme DEVICE Application filed April 14, 1930. Serial No. 444,040.

This invention relates to sound propagating devices, and more particularly to'devices of the type commonly called a loud speaker.

The invention particularly relates to sound propagating devices having a vibrating diaphragm of substantial area and provides for controlling the tension of the diaphragm whereby the vibration characteristics,'such as the period, degrees of freedom, number and distribution of nodal'points, etc., may be controlled. The diaphra m forms one side of a sound chamber, the other side of which is formed ofa similar vibratile diaphragm hav-, ing similar characteristics. The tension of the second diaphragm is also controlled to vary the sound transmission characteristics thereof in a manner similar to the first mentioned diaphragm. The tensionof the diaphragms, together with the size and relative spacing, also controls the sound transmission characteristics of the chamber formed therebetween, which in conjunction with the two diaphragms determines the quality of the sound transmission and the preferential characteristics of the speaker. For example,

any desired relationship may be obtained between the transmission efliciency of the high and low notes, so that a pleasing resultant effect may he obtained. 7

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed. 7

'Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming a partthereof, in which Fig. 1 is a front elevation of a sound propagatingdevice constructed in accordance with the present invention; I Fig. 2 is alongitudinal section thereof;

Fig. 3 is a transverse section taken on the line 33 of Fig. 1;

Fig. l is a front elevation of a modified form of device; V Fig. 5 is a longitudinal section of the device shown in Fig. 4; and I Fig. 6 is a transverse section taken on the line 6'6 of Fig. 4.

' Like reference characters denote like parts in the several figures of the drawings.

In the 'fOllOWiIlg description and in the claims parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the drawings more in detail the invention is shown as applied to a sound propagating device comprising a frame 10 which may be formed of a plurality of sections. Said frame is constructed of any con venient rigid material, such as metal, wood, phenol condensation product, hard rubber or the like. A pair of diaphragms 11 and 12 are stretched over frame 10 and secured thereto by suitable bolts 13 which extend through said diaphragms and through said frame. Diaphragms 11 and 12 are separated from frame 10 by washers 1 1 which are formed of resilient material, such as felt, whereby the vibrations of the diaphragms are prevented from being transmitted to the frame.- lVas'hers 15, of a similar material, may be interposed between bolts 13 and diaphragms 11 and 12 for a similar purpose. Suitable strips 9 as shown, preferably of metal, is placed between the washers 15 and the bolts 13 to act to receive the bolt heads, and preferdably these strips extend the length of each si e. 1 I

A plurality of bars 16 having a width greater than that of frame 10 are mounted within said frame between. the two diaphragms and are secured to said frame by bolts 17. Said. bars may be drawn toward the frame by applying tension to bolts 17 thereby exerting a wedging effect upon the diaphragms. The 'diaphragms are thus brought under tension which may be controlled by varying the position of bars 16.

Diaphragms 11 and 12 are provided with a plurality of apertures 20 and 21 respectively, which are preferably so positioned that the apertures of one diaphragm are not in alignment with the apertures of the other diaphragm. Direct transmission of sound waves through the diaphragms is thus prevented. Said apertures increase the flexibility of the diaphragm and improve the operation thereof. Diaphragm 11 is also provided with a central aperture 22 of substantial size which is spanned by a bridge 23. Said bridge is provided with a plurality of arms 24 which are secured to the diaphragm 11 by bolts 25 or other suitable means. Bridge 23 may be formed directly in the diaphragm. by cutting out suitable apertures and leaving arms 24. A backing member may be used for reenforcing said arms if desired. The center portion of bridge 23 is connected to the vibrating member of an electromagnetic unit 26, as by link 27. A

particular construction of bridge which may be employed and a manner of connecting the same to the electro-magnetic unit is shown more in detail in my copending application Serial No. 326,262, tiled Dec. 15, 1928,

for acoustic device.

In the operation of the above described sound propagating device, vibrations are imparted to diaphragm 11 from the electromagnetic unit through bridge 23. This causes the diaphragm to vibrate in a manner which is determined by the various characteristics thereof, such as the flexibility of the naterial, tension applied thereto and the arrangement of the various apertures. The diaphragm is capable of freely propagating sound waves in one direction, that is, from the outer surface thereof, whereas the waves propagated from the inner surface pass through the sound chamber and react upon diaphragm 12 causing said diaphragm to vibrate in a similar manner and to reinforce the sound waves produced by diaphragm 11. A. portion of these sound waves are transmitted directly from the face of diaphragm 12. Other waves are transmitted through the apertures in diaphragm 12 and still other sound waves are reflected from said diaphragm and pass through the aperture in diaphragm 11..

The transmission characteristics of the entire device may be controlled by varying the tension of the diaphragms, varying the material from which they are constructed. varying the number and distribution of the aperl tures in said diaphragms, varying the size of the diaphragms and varying the spacing therebetween. By suitably selecting each of the above features any desired transmission characteristic may be obtained. For example, the device may be caused to discriminate against either high or low notes or may be caused to propagate approximately equally all of the notes of the musical scale. As an illustration, it may be noted that an increased depth of the sound chamber causes the device to discriminate against the high notes and thereby lowers the apparent tone of the speaker. The size of the apertures produce a similar effect, the small apertures tending to lower the apparent tone of the speaker, whereas large apertures which provide a comparatively large air path, permit the high notes to be more efliciently transmitted and thereby raise the apparent tone of the device. The high frequency response is also accentuated by using diaphragms in small area and vice versa.

The diaphragms may be formed of an 1 thin flexible material, such as thin lightwood, preferably hard wood, which may be laminated and so constructed that the grains for various layers run transversely whereby directional weakness in the wood is prevented. Thin sheet metals may also be used. The bridge is preferably formed of a metal having considerable stiffness, as more fully set forth in my copending application above mentioned. The bars may be made of any rigid wood or metal. It is to be noted that these bars, in addition to controlling the tension of the diaphragm, serve to a certain extent to transmit vibrations between the diaphragms. It is accordingly preferable that these bars, as well as the diaphragms themselves be formed of light material whereby the inertia of the device is reduced to a mini mum.

Referring to the form of invention shown in Figs. 4 to 6, a pair of diaphragms 80, 31 are mounted on a frame 32 which is constructed in a manner similar to frame 10 above described. Said diaphragms are secured to frame 32 by bolts 33 and metallic elongated strips or washers 9 and are separated therefrom by washers 34 of felt or similar material. Bars 35, which are formed similar to bars 16, are secured to frame by bolts 86. Diaphragm 30 is directly connected to an electro-magnetic unit 37 by means of a link 38. Diaphragm 31 is provided with a plurality of apertures 39 for the purpose similar to apertures 21 of diaphragm 12. It is to be noted that in this form of the invention, diaphragm 30 is formed with a continuous surface and the electro-magnetic unit is directly connected thereto. Inasmuch as the central aperture is omitted, the bridge may also be omitted whereby the vibrations are applied directly to the center part of the diaphragm instead of to a substantial area thereof surrounding the central aperture as in Figs. 1 to 3.

It is obvious that diaphragm 30 may be formed with apertures if desired or the apertures may be omitted from diaphragm 31. One form is disclosed merely by way of illustration. It is further to be noted that the size and shape of the device may be varied. The forms illustrated are the preferred forms, but are not to be considered as limitations.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art Without departing from the spirit of the invention.

Vhat is claimed is:

1. A sound propagating device comprising a frame, diaphragms mounted on opposite sides of said frame, members having a width greater than said frame mounted between said diaphragms and means for drawing said members apart from each other and toward said frame for applying tension to said diaphragms.

2. A sound propagating device comprising a pair of diaphragms mounted on a framework to form a chamber, means for controlling the tension of said diaphragms for varying the sound transmission characteristics thereof, said diaphragms having apertures, the size and position of which assist in controlling the transmission characteristics thereof.

3. A sound propagating device comprising a pair of diaphragms spaced to definea chamber, said diaphragms having apertures, a central aperture in one of said diaphragms, a bridge member secured across said central aperture, an actuating means associated with said bridge member for moving the same, the size and spacing of said diaphragms and the size and arrangement of said apertures serving to determine the sound propagating characteristics of said device.

4. A sound propagating device comprising a pair of diaphragms spaced to define a chamber, said diaphragms having apertures, a central aperture in one of said diaphragms, a bridge member secured across said central aperture, actuating means associated with said bridge member for moving the same, the size and spacing of said diaphragms and the size and arrangement of said apertures serving to determine the sound propagating characteristics of said device, and means for adjusting the tension of said diaphragms whereby the characteristics thereof may be further controlled.

5. A sound propagating device comprising a pair of diaphragms spaced to define a chamber, said diaphragms having unaligned apertures, a central aperture in one of said diaphragms, a bridge member secured across said central aperture, actuating means associated with said bridge member for moving the same, the size and spacing of said diaphragms and the size and arrangement of said apertures serving to determine the sound propagating characteristics of said device, and members interposed between said diaphragms and movable relative thereto for applying controllable tension to said diaphragms.

6. A sound propagating device comprising a frame, a pair of diaphragms mounted on said frame, flexible members interposed between said diaphragms and said frame whereby transmission of vibrations therebetween is prevented and means for controlling the tension of said diaphragms. I

7. A sound propagating device comprising a framework, a pair of diaphragms carried thereby, means for preventing transfer of vibrations between said diaphragms and said framework, and tensioning members wider than said framework mounted between said diaphragms and adjustable means for securing said members to said framework for controlling the tension of said diaphragms, said diaphragms having unaligned apertures'and means for imparting sound vibrations to one of said diaphragms.

8. In a sound propagating device comprising an apertured diaphragm, a second member forming in connection therewith a sound chamber, said second member being apertured to pass sound waves and means for vibrating said diaphragm.

9. A sound propagating device comprising a diaphragm stretched over a framework, a vibrating device connected to the center portion thereof and a plurality of apertures formed between said device and said framework for increasing the flexibility of said diaphragm.

This specification signed this 7th day of April, 1929.

ABRAHAM J. FLECK. 

